Investigation of Thermal and Energy Performance of the Thermal Bridge Breaker for Reinforced Concrete Residential Buildings

: Thermal bridges in building envelopes can cause signiﬁcant heat loss and heat gain. In this study, the developed thermal bridge breaker was applied to an interior insulation ﬁnishing system in residential buildings to minimize the thermal bridges in building envelopes. To investigate the thermal and energy performance of the developed thermal bridge breaker, the surface temperatures and heat ﬂow at the wall and ﬂoor junctions were predicted using Physibel. In addition, the heating and cooling energy consumption in a residential building was analyzed by EnergyPlus. As a result, the use of the thermal bridge breaker can minimize the effective thermal transmittance in the building envelope system. Moreover, when the building envelopes were equipped with the thermal bridge breaker, the heating and cooling load through the exterior walls was decreased by 15–27%. Thus, the thermal bridge breaker can play an important role in minimizing the heat loss and occurrence of condensation in building envelopes.


Introduction
Globally, one-third of the total energy consumption is consumed by buildings accompanied by the rapid increase in CO 2 emissions [1][2][3]. Current studies report that the energy consumed by buildings has kept increasing significantly, and in the foreseeable future, it will become of notable concern [4][5][6][7]. Dong et al. [8] observe that the energy consumption in buildings can be remarkably reduced with only a slight improvement in the building energy efficiency. Thus, it is important to find ways to improve the energy efficiency in buildings. In South Korea, the energy consumption of buildings has also become a major issue. According to the "Energy Statistics Handbook in 2020", provided by the Korea Energy Agency [9], about 20% of total energy is consumed by buildings. Among building types, nearly 40% of the total building energy consumption is consumed by residential buildings [9]. Concerning the improvement in building energy efficiency, the Korean government has developed a renewable energy policy to achieve the goal of producing 20% of total electricity by implementing green technologies by 2030 [10][11][12]. In 2018, "The Amendment Plan of 2030 GHG Reduction Roadmap" was also released to reduce GHG emissions by 9.6 million tons of CO 2 , by improving building energy efficiency [13,14]. With regard to the reduction in building energy and GHG emissions, several policies, such as building energy efficiency and zero energy buildings, have also been developed.
To achieve the goal of net or nearly zero energy buildings, several design strategies are needed that combine passive and active design solutions, and renewable energy systems. As one of the passive design strategies, improvements in building envelopes' performance can provide the potential for reductions in energy consumption, as well as improvements in Figure 1 shows the developed thermal bridge breaker in an interior insulation finishing system, to minimize the thermal bridge between an exterior wall and a concrete slab. Specifically, it is a complete system, where 150 mm insulation boards and 50 mm concrete (ultra-high-performance concrete, UHPC) ribbed slabs alternate. In addition, each concrete slab in the developed thermal bridge breaker is connected with a reinforcing bar, as shown  Figure 1. One module is composed of five insulation boards and concrete slabs, and the length of a module is 1 m. Figure 1 shows the developed thermal bridge breaker in an interior insulatio ing system, to minimize the thermal bridge between an exterior wall and a concr Specifically, it is a complete system, where 150 mm insulation boards and 50 mm c (ultra-high-performance concrete, UHPC) ribbed slabs alternate. In addition, ea crete slab in the developed thermal bridge breaker is connected with a reinforcing shown in Figure 1. One module is composed of five insulation boards and concre and the length of a module is 1 m.  Figure 2 shows that the connection between the exterior wall and the concret a building is equipped with a thermal bridge breaker to test the performance of t mal bridge breaker, where this structure is constructed based on the design guide building energy efficiency provided by the Korea Energy Agency [38]. In detail, and 30 mm insulation boards for the wall and slab were used, respectively. Addi the insulation board (thickness: 15 mm, depth: 450 mm) was located in the ceiling severe thermal bridges might occur. The use of additional insulation boards in th is generally recommended for the construction of residential buildings in South K prevent condensation by the thermal bridge.   Figure 2 shows that the connection between the exterior wall and the concrete slab in a building is equipped with a thermal bridge breaker to test the performance of the thermal bridge breaker, where this structure is constructed based on the design guidelines for building energy efficiency provided by the Korea Energy Agency [38]. In detail, 190 mm and 30 mm insulation boards for the wall and slab were used, respectively. Additionally, the insulation board (thickness: 15 mm, depth: 450 mm) was located in the ceiling, where severe thermal bridges might occur. The use of additional insulation boards in the ceiling is generally recommended for the construction of residential buildings in South Korea, to prevent condensation by the thermal bridge. Figure 1 shows the developed thermal bridge breaker in an interior insulation fi ing system, to minimize the thermal bridge between an exterior wall and a concrete Specifically, it is a complete system, where 150 mm insulation boards and 50 mm con (ultra-high-performance concrete, UHPC) ribbed slabs alternate. In addition, each crete slab in the developed thermal bridge breaker is connected with a reinforcing b shown in Figure 1. One module is composed of five insulation boards and concrete and the length of a module is 1 m.  Figure 2 shows that the connection between the exterior wall and the concrete s a building is equipped with a thermal bridge breaker to test the performance of the mal bridge breaker, where this structure is constructed based on the design guidelin building energy efficiency provided by the Korea Energy Agency [38]. In detail, 190 and 30 mm insulation boards for the wall and slab were used, respectively. Addition the insulation board (thickness: 15 mm, depth: 450 mm) was located in the ceiling, w severe thermal bridges might occur. The use of additional insulation boards in the ce is generally recommended for the construction of residential buildings in South Kor prevent condensation by the thermal bridge.    -dimensional model of a thermal bridge breaker at the  joint between the slab and wall. The Physibel program, based on ISO 10211 [39], is a building physics software for analyzing heat transfer in building façade elements, and can be used for various applications, such as building energy performance and condensation control [40][41][42][43]. Using this software, the present study predicted the surface temperatures of the slab and walls, and calculated the heat loss. To analyze the thermal performance of the developed thermal bridge breaker more accurately, the size of the model created by Physibel was at least 1 m, where the structure and building materials were used for typical residential buildings in South Korea. Figure 3 presents the three-dimensional model of a thermal bridge breake between the slab and wall. The Physibel program, based on ISO 10211 [39], i physics software for analyzing heat transfer in building façade elements, and for various applications, such as building energy performance and condensa [40][41][42][43]. Using this software, the present study predicted the surface tempera slab and walls, and calculated the heat loss. To analyze the thermal perform developed thermal bridge breaker more accurately, the size of the model creat bel was at least 1 m, where the structure and building materials were used residential buildings in South Korea.  Table 1 and Figure 2 show the thickness and thermal conductivities of t envelopes. Among these values, the 30 mm thickness insulation for the slab w to prevent heat loss, as well as for noise control at the floor construction, b building energy standard in South Korea [38].   Table 1 and Figure 2 show the thickness and thermal conductivities of the building envelopes. Among these values, the 30 mm thickness insulation for the slab was intended to prevent heat loss, as well as for noise control at the floor construction, based on the building energy standard in South Korea [38].  Table 2 shows the cases for the analysis of the thermal performance of the walls and slabs with/without the thermal bridge breaker and rebar. The thermal performance of the structure was calculated by the thickness and thermal conductivity of the building materials. Case 1 presents the general concrete structure, composed of an exterior wall and a slab. To analyze the thermal influence of rebars, the structure was equipped with rebars (Case 2). In general, the rebars are distributed at regular intervals. For the present study, the simulations were conducted with and without rebars to determine how the rebar can influence the thermal bridge (Case 1 and Case 2). For Case 3, the structure with rebars was equipped with the thermal bridge breaker, as shown in Figure 1. The rebar distribution for Case 2 was based on the guidelines for the construction of residential buildings. structure was calculated by the thickness and thermal conductivity of the building materials. Case 1 presents the general concrete structure, composed of an exterior wall and a slab. To analyze the thermal influence of rebars, the structure was equipped with rebars (Case 2). In general, the rebars are distributed at regular intervals. For the present study, the simulations were conducted with and without rebars to determine how the rebar can influence the thermal bridge (Case 1 and Case 2). For Case 3, the structure with rebars was equipped with the thermal bridge breaker, as shown in Figure 1. The rebar distribution for Case 2 was based on the guidelines for the construction of residential buildings. For the simulation condition, the temperatures for the indoor and outdoor were set at 25 °C and −15 °C, respectively. These thermal conditions were based on the design guidelines for residential buildings for preventing condensation in Korea [44]. Table 3 shows the interior surface temperatures, heat flow and effective thermal transmittance for each case. As shown in Case 2, the surface temperature for the wall and floor junctions was about 21.0 °C, which was the lowest temperature on the upper part of the model. In addition, the surface temperature of the upper part of Case 2 differed by about 2 °C.

Simulation Results
For the lower part of the model, the lowest temperature, about 14.3 °C (Case 2), was observed at the wall and floor junctions, where the end of the insulation was at the ceiling to protect against condensation (width: 450 mm, thickness: 15 mm). It can be observed that condensation can easily occur in this situation, when the relative humidity is above 52%. Moreover, the surface temperatures of Case 2 at the ceiling show about 8.8 °C difference between the floor and wall junctions (14.3 °C), and the corner of the walls (23.1 °C). Furthermore, 92.6 W/m 2 of the heat loss occurred at the wall and floor junctions at the ceiling in Case 2. Compared with Case 3, a large surface temperature difference was observed at the lower part, due to the influence of the thermal bridge breaker, which was 14.3 °C and 19.4 °C for Case 2 and 3, respectively. For residential buildings in South Korea, it can be observed that the installation of the thermal bridge breaker can minimize the heat loss and condensation occurrence at the wall and floor junctions. To analyze the energy consumption using the thermal bridge breaker, the effective thermal transmittance was calculated. When simply calculating the thermal transmittance of the wall in all cases, it was 0.144 W/m 2 K. However, the effective thermal transmittance considering the thermal bridge increased higher about 0.1 W/m 2 K when three-dimensional modeling was used (0.241 W/m 2 K).
For Case 2, where reinforcing bars were installed, the effective thermal transmittance was 0.241 W/m 2 K. For Case 1, where an assumption was made that no reinforcing bar was installed, it was 0.234 W/m 2 K, which showed that the thermal performance of Case 1 was better than that of Case 2, by 0.007 W/m 2 K. When the developed thermal bridge breaker Energies 2022, 15, x FOR PEER REVIEW 5 of 11 structure was calculated by the thickness and thermal conductivity of the building materials. Case 1 presents the general concrete structure, composed of an exterior wall and a slab. To analyze the thermal influence of rebars, the structure was equipped with rebars (Case 2). In general, the rebars are distributed at regular intervals. For the present study, the simulations were conducted with and without rebars to determine how the rebar can influence the thermal bridge (Case 1 and Case 2). For Case 3, the structure with rebars was equipped with the thermal bridge breaker, as shown in Figure 1. The rebar distribution for Case 2 was based on the guidelines for the construction of residential buildings.

Case 1 Case 2 Case 3
Thermal bridge breaker uninstall uninstall install rebar uninstall install install For the simulation condition, the temperatures for the indoor and outdoor were set at 25 °C and −15 °C, respectively. These thermal conditions were based on the design guidelines for residential buildings for preventing condensation in Korea [44]. Table 3 shows the interior surface temperatures, heat flow and effective thermal transmittance for each case. As shown in Case 2, the surface temperature for the wall and floor junctions was about 21.0 °C, which was the lowest temperature on the upper part of the model. In addition, the surface temperature of the upper part of Case 2 differed by about 2 °C.

Simulation Results
For the lower part of the model, the lowest temperature, about 14.3 °C (Case 2), was observed at the wall and floor junctions, where the end of the insulation was at the ceiling to protect against condensation (width: 450 mm, thickness: 15 mm). It can be observed that condensation can easily occur in this situation, when the relative humidity is above 52%. Moreover, the surface temperatures of Case 2 at the ceiling show about 8.8 °C difference between the floor and wall junctions (14.3 °C), and the corner of the walls (23.1 °C). Furthermore, 92.6 W/m 2 of the heat loss occurred at the wall and floor junctions at the ceiling in Case 2. Compared with Case 3, a large surface temperature difference was observed at the lower part, due to the influence of the thermal bridge breaker, which was 14.3 °C and 19.4 °C for Case 2 and 3, respectively. For residential buildings in South Korea, it can be observed that the installation of the thermal bridge breaker can minimize the heat loss and condensation occurrence at the wall and floor junctions. To analyze the energy consumption using the thermal bridge breaker, the effective thermal transmittance was calculated. When simply calculating the thermal transmittance of the wall in all cases, it was 0.144 W/m 2 K. However, the effective thermal transmittance considering the thermal bridge increased higher about 0.1 W/m 2 K when three-dimensional modeling was used (0.241 W/m 2 K).
For Case 2, where reinforcing bars were installed, the effective thermal transmittance was 0.241 W/m 2 K. For Case 1, where an assumption was made that no reinforcing bar was installed, it was 0.234 W/m 2 K, which showed that the thermal performance of Case 1 was better than that of Case 2, by 0.007 W/m 2 K. When the developed thermal bridge breaker Energies 2022, 15, x FOR PEER REVIEW 5 of 11 structure was calculated by the thickness and thermal conductivity of the building materials. Case 1 presents the general concrete structure, composed of an exterior wall and a slab. To analyze the thermal influence of rebars, the structure was equipped with rebars (Case 2). In general, the rebars are distributed at regular intervals. For the present study, the simulations were conducted with and without rebars to determine how the rebar can influence the thermal bridge (Case 1 and Case 2). For Case 3, the structure with rebars was equipped with the thermal bridge breaker, as shown in Figure 1. The rebar distribution for Case 2 was based on the guidelines for the construction of residential buildings.

Case 1 Case 2 Case 3
Thermal bridge breaker uninstall uninstall install rebar uninstall install install For the simulation condition, the temperatures for the indoor and outdoor were set at 25 °C and −15 °C, respectively. These thermal conditions were based on the design guidelines for residential buildings for preventing condensation in Korea [44]. Table 3 shows the interior surface temperatures, heat flow and effective thermal transmittance for each case. As shown in Case 2, the surface temperature for the wall and floor junctions was about 21.0 °C, which was the lowest temperature on the upper part of the model. In addition, the surface temperature of the upper part of Case 2 differed by about 2 °C.

Simulation Results
For the lower part of the model, the lowest temperature, about 14.3 °C (Case 2), was observed at the wall and floor junctions, where the end of the insulation was at the ceiling to protect against condensation (width: 450 mm, thickness: 15 mm). It can be observed that condensation can easily occur in this situation, when the relative humidity is above 52%. Moreover, the surface temperatures of Case 2 at the ceiling show about 8.8 °C difference between the floor and wall junctions (14.3 °C), and the corner of the walls (23.1 °C). Furthermore, 92.6 W/m 2 of the heat loss occurred at the wall and floor junctions at the ceiling in Case 2. Compared with Case 3, a large surface temperature difference was observed at the lower part, due to the influence of the thermal bridge breaker, which was 14.3 °C and 19.4 °C for Case 2 and 3, respectively. For residential buildings in South Korea, it can be observed that the installation of the thermal bridge breaker can minimize the heat loss and condensation occurrence at the wall and floor junctions. To analyze the energy consumption using the thermal bridge breaker, the effective thermal transmittance was calculated. When simply calculating the thermal transmittance of the wall in all cases, it was 0.144 W/m 2 K. However, the effective thermal transmittance considering the thermal bridge increased higher about 0.1 W/m 2 K when three-dimensional modeling was used (0.241 W/m 2 K).
For Case 2, where reinforcing bars were installed, the effective thermal transmittance was 0.241 W/m 2 K. For Case 1, where an assumption was made that no reinforcing bar was installed, it was 0.234 W/m 2 K, which showed that the thermal performance of Case 1 was better than that of Case 2, by 0.007 W/m 2 K. When the developed thermal bridge breaker structure was calculated by the thickness and thermal conductivity of the building materials. Case 1 presents the general concrete structure, composed of an exterior wall and a slab. To analyze the thermal influence of rebars, the structure was equipped with rebars (Case 2). In general, the rebars are distributed at regular intervals. For the present study, the simulations were conducted with and without rebars to determine how the rebar can influence the thermal bridge (Case 1 and Case 2). For Case 3, the structure with rebars was equipped with the thermal bridge breaker, as shown in Figure 1. The rebar distribution for Case 2 was based on the guidelines for the construction of residential buildings. For the simulation condition, the temperatures for the indoor and outdoor were set at 25 °C and −15 °C, respectively. These thermal conditions were based on the design guidelines for residential buildings for preventing condensation in Korea [44]. Table 3 shows the interior surface temperatures, heat flow and effective thermal transmittance for each case. As shown in Case 2, the surface temperature for the wall and floor junctions was about 21.0 °C, which was the lowest temperature on the upper part of the model. In addition, the surface temperature of the upper part of Case 2 differed by about 2 °C.

Simulation Results
For the lower part of the model, the lowest temperature, about 14.3 °C (Case 2), was observed at the wall and floor junctions, where the end of the insulation was at the ceiling to protect against condensation (width: 450 mm, thickness: 15 mm). It can be observed that condensation can easily occur in this situation, when the relative humidity is above 52%. Moreover, the surface temperatures of Case 2 at the ceiling show about 8.8 °C difference between the floor and wall junctions (14.3 °C), and the corner of the walls (23.1 °C). Furthermore, 92.6 W/m 2 of the heat loss occurred at the wall and floor junctions at the ceiling in Case 2. Compared with Case 3, a large surface temperature difference was observed at the lower part, due to the influence of the thermal bridge breaker, which was 14.3 °C and 19.4 °C for Case 2 and 3, respectively. For residential buildings in South Korea, it can be observed that the installation of the thermal bridge breaker can minimize the heat loss and condensation occurrence at the wall and floor junctions. To analyze the energy consumption using the thermal bridge breaker, the effective thermal transmittance was calculated. When simply calculating the thermal transmittance of the wall in all cases, it was 0.144 W/m 2 K. However, the effective thermal transmittance considering the thermal bridge increased higher about 0.1 W/m 2 K when three-dimensional modeling was used (0.241 W/m 2 K).
For Case 2, where reinforcing bars were installed, the effective thermal transmittance was 0.241 W/m 2 K. For Case 1, where an assumption was made that no reinforcing bar was installed, it was 0.234 W/m 2 K, which showed that the thermal performance of Case 1 was better than that of Case 2, by 0.007 W/m 2 K. When the developed thermal bridge breaker For the simulation condition, the temperatures for the indoor and outdoor were set at 25 • C and −15 • C, respectively. These thermal conditions were based on the design guidelines for residential buildings for preventing condensation in Korea [44]. Table 3 shows the interior surface temperatures, heat flow and effective thermal transmittance for each case. As shown in Case 2, the surface temperature for the wall and floor junctions was about 21.0 • C, which was the lowest temperature on the upper part of the model. In addition, the surface temperature of the upper part of Case 2 differed by about 2 • C.

Simulation Results
For the lower part of the model, the lowest temperature, about 14.3 • C (Case 2), was observed at the wall and floor junctions, where the end of the insulation was at the ceiling to protect against condensation (width: 450 mm, thickness: 15 mm). It can be observed that condensation can easily occur in this situation, when the relative humidity is above 52%. Moreover, the surface temperatures of Case 2 at the ceiling show about 8.8 • C difference between the floor and wall junctions (14.3 • C), and the corner of the walls (23.1 • C). Furthermore, 92.6 W/m 2 of the heat loss occurred at the wall and floor junctions at the ceiling in Case 2. Compared with Case 3, a large surface temperature difference was observed at the lower part, due to the influence of the thermal bridge breaker, which was 14.3 • C and 19.4 • C for Case 2 and 3, respectively. For residential buildings in South Korea, it can be observed that the installation of the thermal bridge breaker can minimize the heat loss and condensation occurrence at the wall and floor junctions. To analyze the energy consumption using the thermal bridge breaker, the effective thermal transmittance was calculated. When simply calculating the thermal transmittance of the wall in all cases, it was 0.144 W/m 2 K. However, the effective thermal transmittance considering the thermal bridge increased higher about 0.1 W/m 2 K when three-dimensional modeling was used (0.241 W/m 2 K). The upper part of the model was equipped in the structure (Case 3), the effective thermal transmittance was 0 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge brea can have a significant impact on the thermal insulation performance. In the next sect Case 2 and 3 were applied to the apartment building in South Korea, to investigate energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the ther bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dim was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen-was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen- The lower part of the model was equipped in the structure (Case 3), the effective thermal transmittance was 0 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than tha Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge bre can have a significant impact on the thermal insulation performance. In the next sec Case 2 and 3 were applied to the apartment building in South Korea, to investigate energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the the bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dim was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen-was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen-

Heat loss [W/m 2 ]
The upper part of the model was equipped in the structure (Case 3), the effective thermal transmittance was 0 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than tha Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge bre can have a significant impact on the thermal insulation performance. In the next sec Case 2 and 3 were applied to the apartment building in South Korea, to investigate energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the the bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dim was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen-was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen- The lower part of the model was equipped in the structure (Case 3), the effective thermal transmittance was 0 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge bre can have a significant impact on the thermal insulation performance. In the next sec Case 2 and 3 were applied to the apartment building in South Korea, to investigate energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the ther bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dim was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen-was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and three-dimen- For Case 2, where reinforcing bars were installed, the effective thermal transmittance was 0.241 W/m 2 K. For Case 1, where an assumption was made that no reinforcing bar was installed, it was 0.234 W/m 2 K, which showed that the thermal performance of Case 1 was better than that of Case 2, by 0.007 W/m 2 K. When the developed thermal bridge breaker was equipped in the structure (Case 3), the effective thermal transmittance was 0.174 W/m 2 K. In addition, the effective thermal transmittance in Case 3 was lower than that in Case 2, about 0.067 W/m 2 K. It can be observed that the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance. In the next section, Case 2 and 3 were applied to the apartment building in South Korea, to investigate the energy performance.

Simulation Setup
To analyze the energy performance of the apartment unit equipped with the thermal bridge breaker, EnergyPlus 9.3.0 was used [45]. Figure 4 shows the plan and threedimensional view of the residential building for this analysis. The model was created by OpenStudio [46]. As the standard unit size of residential buildings, the size of the unit was 84 m 2 and each floor had four units. To consider the heat transfer among floors, the energy simulation models with three floors were created, and Units 1 and 2 in the middle of the floors were the main focus for the analysis.  It was assumed that the residential building was located in Seoul in South Korea. The other boundary conditions are presented in Table 4. The simulation was conducted over a period of a year.

The Result of the Simulation for Heating and Cooling Analysis
The effective thermal transmittances for the exterior walls in Unit ① in Figure 4 were set to 0.241 W/m 2 K and 0.174 W/m 2 K for heating and cooling loads, respectively. As a result of the simulation, Figure 5 shows the cooling and heating loads for the components at Unit ①. As shown in (a) within Figure 5, the cooling load was measured at 3920 W, when the effective thermal transmittance of 0.174 W/m 2 K was applied to the exterior walls of Unit ①. Through the exterior walls, 159 W was gained, which consisted of 4.1% of the total cooling load. Around 47% of the heat (1840 W) was gained through window systems, and, thus, a way to improve the thermal performance of the window systems is required, in order to reduce the cooling load. In the case of heating, the total heating load was 3577 W, as shown in (b) of Figure 5. An estimated 12% of heat (439 W) was lost through the exterior walls. Specifically, the heat losses from ventilation and infiltration were measured at 64% and 15%, respectively. Additionally, 17% and 5% of the total heating load were lost through the window system and the entrance door, respectively. Overall, the heating load has different aspects from the cooling load.
To investigate thermal influence through the thermal bridge breaker, a heating and cooling analysis was conducted. The effective thermal transmittance of 0.241 W/m 2 K was It was assumed that the residential building was located in Seoul in South Korea. The other boundary conditions are presented in Table 4. The simulation was conducted over a period of a year.

The Result of the Simulation for Heating and Cooling Analysis
The effective thermal transmittances for the exterior walls in Unit 1 in Figure 4 were set to 0.241 W/m 2 K and 0.174 W/m 2 K for heating and cooling loads, respectively. As a result of the simulation, Figure 5 shows the cooling and heating loads for the components at Unit 1 . As shown in (a) within Figure 5, the cooling load was measured at 3920 W, when the effective thermal transmittance of 0.174 W/m 2 K was applied to the exterior walls of Unit 1 . Through the exterior walls, 159 W was gained, which consisted of 4.1% of the total cooling load. Around 47% of the heat (1840 W) was gained through window systems, and, thus, a way to improve the thermal performance of the window systems is required, in order to reduce the cooling load. In the case of heating, the total heating load was 3577 W, as shown in (b) of Figure 5. An estimated 12% of heat (439 W) was lost through the exterior walls. Specifically, the heat losses from ventilation and infiltration were measured at 64% and 15%, respectively. Additionally, 17% and 5% of the total heating load were lost through the window system and the entrance door, respectively. Overall, the heating load has different aspects from the cooling load. applied to Unit ①, without the thermal bridge breaker, while the effective thermal transmittance of 0.174 W/m 2 K was used for Unit ①, which was equipped with the thermal bridge breaker. The heating load for Unit ①, with/without the thermal bridge breaker, was measured at 3744 W and 3577 W, respectively. This reveals that a 4.5% decrease in the heating energy occurred when the thermal bridge breaker was equipped. For cooling energy, an estimated 0.7% increase was observed when the thermal bridge breaker was used. It can be observed that the heat gained through the exterior walls in the summer was smaller than the heat lost through the walls in the winter. To investigate thermal influence through the thermal bridge breaker, a heating and cooling analysis was conducted. The effective thermal transmittance of 0.241 W/m 2 K was applied to Unit 1 , without the thermal bridge breaker, while the effective thermal transmittance of 0.174 W/m 2 K was used for Unit 1 , which was equipped with the thermal bridge breaker. The heating load for Unit 1 , with/without the thermal bridge breaker, was measured at 3744 W and 3577 W, respectively. This reveals that a 4.5% decrease in the heating energy occurred when the thermal bridge breaker was equipped. For cooling energy, an estimated 0.7% increase was observed when the thermal bridge breaker was used. It can be observed that the heat gained through the exterior walls in the summer was smaller than the heat lost through the walls in the winter.
In the case of Unit 2 , the size of the exterior walls was 67.8 m 2 , while the size of the exterior walls of Unit 1 was 100.4 m 2 . When the thermal bridge breaker for Unit 2 was used, an estimated 2.9% decrease in the heating load was observed. This reveals that the reduction in heating load in the unit equipped with the thermal bridge breaker can be greater when the area of the exterior walls is larger. Figure 6 presents the cooling and heating loads through the exterior walls with the thermal bridge breaker, since the exterior wall was the main component thermally influenced by the thermal bridge breaker. When the developed thermal breaker was used, the heat gain through the exterior walls in the summer decreased from 188.7 W to 159.1 W, which was about 15.7%. In the winter, the heat loss through the exterior walls was reduced from 600 W to 439 W (about 26.9%). In sum, the use of the thermal bridge breaker can improve thermal performance, such as heating and cooling, by 15-27% for residential buildings equipped with an interior insulating finishing system. In the case of Unit ②, the size of the exterior walls was 67.8 m 2 , while the size of the exterior walls of Unit ① was 100.4 m 2 . When the thermal bridge breaker for Unit ② was used, an estimated 2.9% decrease in the heating load was observed. This reveals that the reduction in heating load in the unit equipped with the thermal bridge breaker can be greater when the area of the exterior walls is larger. Figure 6 presents the cooling and heating loads through the exterior walls with the thermal bridge breaker, since the exterior wall was the main component thermally influenced by the thermal bridge breaker. When the developed thermal breaker was used, the heat gain through the exterior walls in the summer decreased from 188.7 W to 159.1 W, which was about 15.7%. In the winter, the heat loss through the exterior walls was reduced from 600 W to 439 W (about 26.9%). In sum, the use of the thermal bridge breaker can improve thermal performance, such as heating and cooling, by 15-27% for residential buildings equipped with an interior insulating finishing system.

Conclusions
The present study investigated the thermal and energy performances of the developed thermal bridge breaker for residential buildings constructed using reinforced concrete, to minimize the thermal bridges in building envelopes. By using Physibel, thermal behaviors with/without the thermal bridge breaker, such as interior surface temperatures, heat flow, and effective thermal transmittance, were calculated. Among the cases, the effective thermal transmittance was the lowest when the developed thermal bridge breaker was equipped. It can be observed that the use of the thermal bridge breaker can have a significant impact on thermal insulation performance, as well as improve the thermal performance. In the case of the cooling and heating load analysis, the EnergyPlus program was utilized. In general, heat was greatly lost through the exterior walls in the winter, while heat was significantly gained through the window systems in the summer. When the thermal bridge breaker was equipped, the total heating was decreased by 4.5%, while the cooling load was increased by 0.7%. Specifically, the heating and cooling load through the exterior walls with the thermal bridge breaker was decreased by 15-27%. Therefore,

Conclusions
The present study investigated the thermal and energy performances of the developed thermal bridge breaker for residential buildings constructed using reinforced concrete, to minimize the thermal bridges in building envelopes. By using Physibel, thermal behaviors with/without the thermal bridge breaker, such as interior surface temperatures, heat flow, and effective thermal transmittance, were calculated. Among the cases, the effective thermal transmittance was the lowest when the developed thermal bridge breaker was equipped. It can be observed that the use of the thermal bridge breaker can have a significant impact on thermal insulation performance, as well as improve the thermal performance. In the case of the cooling and heating load analysis, the EnergyPlus program was utilized. In general, heat was greatly lost through the exterior walls in the winter, while heat was significantly gained through the window systems in the summer. When the thermal bridge breaker was equipped, the total heating was decreased by 4.5%, while the cooling load was increased by 0.7%. Specifically, the heating and cooling load through the exterior walls with the thermal bridge breaker was decreased by 15-27%. Therefore, the use of the thermal bridge breaker can have a significant impact on the thermal insulation performance, and can also reduce the building energy consumption.